Qiu Quan-Sheng
a MOE Key Laboratory of Cell Activities and Stress Adaptations, School of Life Sciences, Lanzhou University , Lanzhou , Gansu , China.
Plant Signal Behav. 2016 May 3;11(5):e1147643. doi: 10.1080/15592324.2016.1147643.
The Arabidopsis NHX antiporter family contains eight members that are divided into three subclasses: vacuolar, endosomal, and plasma membrane. While the plasma membrane and vacuolar NHXs have been studied extensively, the activity and function of the endosomal NHXs are beginning to be discovered. AtNHX5 and AtNHX6 are endosomal Na(+),K(+)/H(+) antiporters that share high sequence similarity. They are localized in the Golgi, trans-Golgi network (TGN), and prevacuolear compartment (PVC). Studies have shown that AtNHX5 and AtNHX6 mediate K(+) and Na(+) transport, and regulate cellular pH homeostasis. Sequence alignment has found that AtNHX5 and AtNHX6 contain four conserved acidic amino acid residues in transmembrane domains that align with yeast and human NHXs. Three of these conserved acidic residues are critical for K(+) transport and seedling growth in Arabidopsis. Moreover, studies have shown that the precursors of the seed storage proteins are missorted to the apoplast in the nhx5 nhx6 knockout mutant, suggesting that AtNHX5 and AtNHX6 regulate protein transport into the vacuole. Further analysis found that AtNHX5 and AtNHX6 regulated the binding of VSR to its cargoes. Taken together, AtNHX5 and AtNHX6 play an important role in cellular ion and pH homeostasis, and are essential for protein transport into the vacuole.
拟南芥NHX反向转运蛋白家族包含八个成员，分为三个亚类：液泡型、内体型和质膜型。虽然质膜型和液泡型NHX已得到广泛研究，但内体型NHX的活性和功能才刚刚开始被发现。AtNHX5和AtNHX6是内体Na(+)、K(+)/H(+)反向转运蛋白，具有高度的序列相似性。它们定位于高尔基体、反式高尔基体网络（TGN）和前液泡区室（PVC）。研究表明，AtNHX5和AtNHX6介导K(+)和Na(+)转运，并调节细胞pH稳态。序列比对发现，AtNHX5和AtNHX6在跨膜结构域中含有四个保守的酸性氨基酸残基，与酵母和人类的NHX对齐。其中三个保守的酸性残基对拟南芥中的K(+)转运和幼苗生长至关重要。此外，研究表明，种子贮藏蛋白的前体在nhx5 nhx6敲除突变体中被错误分选到质外体，这表明AtNHX5和AtNHX6调节蛋白向液泡的转运。进一步分析发现，AtNHX5和AtNHX6调节VSR与其货物的结合。综上所述，AtNHX5和AtNHX6在细胞离子和pH稳态中起重要作用，并且对于蛋白向液泡的转运至关重要。
